Optical discs are data storage media used to store a wide variety of digitally encoded data. Such discs are usually portable in nature and can be played in a variety of settings such as personal computers, car audio players, home theater systems, handheld personal entertainment devices, home gaming systems, etc.
A typical optical disc comprises a circular disc having one or more data storage (recording) layers of light reflective material embedded in a refractive substrate. Each layer is typically disposed along a plane substantially normal to an axis about which the disc is rotated and stores data in the form of localized areas of different reflectivity (pits and lands). The data can be stored along a continuously extending spiral track or a number of nested concentric tracks.
A data transducing head uses a laser or similar light source to output a readback signal based on the different reflectivities of the pit and land areas. Decoding circuitry decodes the user data for output by the appropriate playback device.
Optical discs can be pre-recorded or recordable. A pre-recorded disc typically includes an embedded metallized layer that stores the respective pits and lands. The metallized layer is formed during manufacturing of the disc using an injection molding process, and the data are permanently embossed in the disc once the disc manufacturing operation is completed.
Recordable discs are media to which data can be written. As used herein, “recordable” covers both discs that can be written once (WORM discs) or written and erased many times (rewritable discs). WORM discs typically utilize an embedded layer of dye or other material that can be selectively exposed to a write laser beam to permanently provide areas of different reflectivities corresponding to the pits and lands. Rewritable discs typically utilize a light beam to write the data as a series of areas of different reflectivity, and a magnetic field to erase the previously written data.
Pre-recorded optical discs have an advantage of low cost per byte of recorded data as long as each byte is the same on each copy of the optical disc. A disadvantage of pre-recorded optical discs is an inability to add some amount of unique information to each disc after the substrate has been manufactured, i.e. serial numbers, product activation codes, software “patches” or updates, etc.
Recordable optical discs have an advantage in that each disc can have unique data values recorded on them. A disadvantage of recordable optical discs is that all of the content data are recorded after manufacturing, thereby increasing the costs per byte. Generally, content suppliers tend to utilize pre-recorded discs for higher volume production runs where throughput efficiencies can be achieved, but are increasingly turning to the use of recordable discs for lower volume production runs.
There have been several attempts to create “hybrid” optical discs where one portion of the disc is pre-recorded and another portion is recordable. One goal of this approach is to take advantage of low cost per byte of pre-recorded data while providing the flexibility to add subsequent information to the disc. Examples of these types of discs include the Kodak® CD-PROM and the ODC™ CDR-ROM. Such discs typically have the pre-recorded portion and the recordable portion manufactured into a single surface of the substrate, which complicates the disc manufacturing process and thereby increases the costs per delivered byte. Other types of hybrid discs arrange the pre-recorded and recordable portions so as to be accessed from opposing sides of the disc, which requires two heads or the disc to be flipped over to access both portions.
Due to the continued demand for content provided on optical discs, there remains a continued need for improved disc formats that are relatively easy and inexpensive to implement, and provide flexibility to accommodate a variety of needs such as tracking and copy protection systems. It is to these and other improvements that the present invention is generally directed.